Tough drives for fast climbers

Nord Drivesystems has been, for more than 15 years, the sole drive supplier of STROS, the largest manufacturer of construction hoists in the Czech Republic.

Eight of the high-rises at “Moscow City”, a major construction project in Russia, are being built or have already been completed with STROS hoists. The hoists reach heights of 300 m or more and have to withstand wind speeds of up to 20 m/s. Safety is therefore fundamental.

STROS specializes in rack-and-pinion mast-climbing equipment which allows for extended service heights and can be quickly installed. The gearbox output shaft is fitted with a gear that meshes with a rack attached to the guide mast. This robust drive method withstands extreme environmental conditions over long time periods. Apart from building equipment hire and construction companies, STROS frequently supplies power plants, industrial plants, and offshore facilities. Completed projects include locations beyond the Arctic Circle and in the tough climatic conditions of the tropics. The NOV series of personnel and material hoists reaches maximum lifting speeds of 100 m/min and load capacities up to 3,200 kg.

Moscow City construction project

The highest hoist to date was erected at the “Moscow City” construction site. The complex consists of several high-rise buildings, eight of which are equipped with STROS hoists. One of the hoists serves the Mercury City Tower which at 340 m is currently the tallest building in Europe. The NOV 2032 hoist has a 350 m lifting height, a 2 ton load capacity and a 70 m/min rating. With a control panel that allows the operator to select the floor number, the hoist provides the same level of control comfort as a standard elevator in an apartment block. The drive unit consists of three helical bevel geared motors with external braking resistors.

“The motors are equipped with electromagnetic disc brakes which can be released by hand”, says STROS chairman Zdenek Coubal. “This is a custom solution from Nord Drivesystems. And it exemplifies our cooperation: whatever new challenges we meet, Nord provides consulting and tests and develops a solution.” A control cabinet inverter with hoist function controls all three motors. It enables soft starts and stops and high leveling precision. Coubal says, “We are working very closely with the construction companies. They say that our technology saves time and money.”

Patented safety device

The STROS engineering team has designed a mechanism to safely stop hoist cages in the event of a failure. If the nominal lowering speed is exceeded, the safety device will trip and engage its pinion with the rack to gradually stop the hoist cage. The centrifugal mechanism is individually set for each machine model. The STROS safety device is certified by the internationally recognized German technical testing authority TÜV SÜD.

Higher requirements

Initially, STROS only used geared motors. As the manufacturer built only relatively slow hoists at that time, start and stop control via the motor switch was fully sufficient at speeds up to 40 m/min. But with the growth of the customer list, the projects grew accordingly. STROS started building hoists for higher and higher buildings. Consequently, the cages had to travel faster to decrease waiting times. New models have rated speeds of 55 to 100 m/min and are always equipped with variable frequency drives. In addition to geared motors, Nord supplies control cabinet inverters that control motor speed and enable precise braking.

Sophisticated positioning and safety functions such as STO and SS1 for safety requirements up to SIL3 are also available.

Another diversification: special and permanent elevators

The 2008 collapse of the construction industry severely affected suppliers such as STROS. To survive, the company sought applications for its technology, apart from construction hoists, and branched into hoists for permanent use on buildings, chimneys, or technological equipment. This new field makes up a large part of STROS projects today. For example, the company built a 150 m high permanent elevator on a chimney at the Siekierki power station in Poland’s capital Warsaw. The NOV 514 elevator has a load capacity of 500 kg and a rated speed of 46 m/min. The elevator was equipped with a frequency inverter which ensures soft starting and braking and includes a POSICON position control. The project was immediately followed by a contract for a second, 200 m high elevator for another chimney at the same plant.

No breakdowns

If a hoist does not work, the entire construction site will come to a standstill. Therefore, the drive must never break down under any circumstances. The Nord concept for STROS hoisting equipment with up to three autonomously working drives prevents costly downtimes. Looking back on 15 years with Nord as their sole drive supplier, STROS Chairman Coubal says, “Nord technology is reliable, and the service is excellent.”

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